Derivative Instruments And Hedging Activities - Narrative (Detail)	12 Months Ended
	Dec. 31, 2015 USD ($) derivative Swap	Dec. 31, 2014 USD ($) derivative Swap	Mar. 31, 2014 USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification from AOCI to interest expense	$ 1,700,000
Termination value of derivatives in a net liability position	14,300,000
Minimum collateral with counterparties	$ 14,300,000
Not Designated as Hedging Instrument | Minimum
Derivative Instruments, Gain (Loss) [Line Items]
Number of days for commitments to expire, lower limit	30 days
Not Designated as Hedging Instrument | Maximum
Derivative Instruments, Gain (Loss) [Line Items]
Number of days for commitments to expire, higher limit	60 days
Not Designated as Hedging Instrument | Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Number of interest rate swaps | Swap	62	44
Derivative notional amount	$ 461,000,000.0	$ 251,900,000.0
Not Designated as Hedging Instrument | Residential mortgage loan commitments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative notional amount	2,800,000.0	3,800,000.0
Not Designated as Hedging Instrument | Credit contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivative notional amount	$ 19,300,000.0	$ 13,400,000.0	$ 19,300,000
Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Number of interest rate swaps | derivative	1	1
Derivative notional amount	$ 150,000,000.0	$ 150,000,000.0	$ 150,000,000